I. Technical Field
The present invention relates to a shaft member for hydrodynamic bearing apparatuses which relatively rotatably supports the shaft member in the radial direction in a non-contact manner by the hydrodynamic effect which occurs in a radial bearing gap, and a method for producing the same.
II. Description of Related Art
A hydrodynamic bearing rotatably supports a shaft member by the hydrodynamic effect of lubricating oil which occurs in a bearing gap in a non-contact manner. For example, the bearing is used in the spindle motor of disk-shaped recording medium drive units such as HDDs incorporated therein. Hydrodynamic bearing apparatuses of this type are provided with a radial bearing portion which rotatably supports a shaft member in the radial direction in a non-contact manner, and a thrust bearing portion which rotatably supports the shaft member in the thrust direction in a non-contact manner. Grooves for producing a hydrodynamic pressure (hydrodynamic grooves) are formed on the inner surface of a bearing sleeve or the outer surface of the shaft member, which constitutes the radial bearing portion. Moreover, hydrodynamic grooves are formed on both end faces of a flange portion of a shaft member which constitutes a thrust bearing portion, or on the face facing it (an end face of the bearing sleeve or an end face of a thrust member fixed on the housing, or the inner bottom face of the bottom of the housing, etc.) (for example, refer to Japanese Unexamined Patent Publication No. 2002-61641).
Moreover, the above hydrodynamic grooves are formed, for example, on the outer surface of the shaft member in a herringbone arrangement or a spiral arrangement. Known examples of methods for forming the hydrodynamic grooves of this type include cutting (for example, refer to Japanese Unexamined Patent Publication No. H08-196056), etching (for example, refer to Japanese Unexamined Patent Publication No. H06-158357), among others.